Minimally invasive surgery is a surgical procedure performed by making a very small incision through which to insert surgical instruments to perform the surgical procedure. A minimally invasive procedure is usually performed in the abdominal region, by inserting a cannula through an abdominal wall of the patient. The cannula provides access to the surgical site for inserting, manipulating and removing the surgical instruments at the interior surgical site. Minimally invasive surgery substantially reduces the amount of trauma to a patient compared to a completely open surgical procedure in which a large incision is made to directly visualize and contact the tissue that the surgical site. In most cases, the time for the patient to recover from the surgery is substantially reduced. In urological surgery performed on or in the bladder, minimally invasive surgery avoids a substantial incision in the wall of the bladder which will complicate and prolong healing.
A dilation instrument, such as a trocar or obturator, is commonly used to place the cannula within the abdominal wall. The trocar or obturator is used to expand an initial small surgical pathway through the abdominal wall into a wider opening to accommodate the larger cannula. The typical dilation procedure involves forcing the trocar or obturator through the small surgical pathway to expand or spread the tissue surrounding the small surgical pathway into the enlarged opening for the cannula. Once the enlarged opening has been formed, the cannula is inserted and the trocar or obturator is removed, leaving a relatively large pathway through the cannula for inserting, manipulating and removing the medical instruments.
Significant physical force is required to spread the surrounding tissue when expanding the small surgical pathway into the enlarged opening. Typically, the leading end of the trocar or the obturator has a pointed or flared configuration which expands the tissue when physically forced through the small surgical pathway. This expansion technique is known as blunt force dilation.
Blunt force dilation usually requires a considerable amount of pushing force to create the enlarged opening. Considerable force is required because the tough, relatively non-expandable characteristics of the exterior skin on the abdominal wall and of a fascia layer located at the internal margin of the abdominal wall creates substantial resistance to expansion of the tissue surrounding the small surgical pathway. A layer of mostly vascular and adipose tissue separates the exterior skin and the interior fascia layer in the abdominal wall, but this intermediate portion does not generally create substantial resistance to expansion. The physically tough and relatively nonexpandable characteristics of the exterior skin and the interior fascia layer are responsible for the considerable force required to accomplish blunt force dilation through the abdominal wall.
To diminish the force necessary to penetrate the exterior skin layer, small enlarging cuts radial cuts are made in the exterior skin surrounding the initial small pathway, usually with a scalpel. However, making similar manual cuts the interior fascia layer is more difficult and engenders significant risks, because such cuts may extend beyond the internal fascia layer into adjacent internal organs and damage those organs. In most cases with minimally invasive surgery in the abdominal area, insuflation expands the abdominal wall away from the adjacent internal organs and tissues sufficiently so that penetrating the internal fascia layer with blunt force dilation usually carries no attendant risk of damaging adjoining internal organs.
Some types of trocars and obturators have cutting surfaces or blades formed on their leading tips to facilitate cutting from the outside through the abdominal wall, including the internal fascia layer. Using trocars and obturators with cutting surfaces and blades carries the risk of unintended deeper penetration into and damage of adjoining internal organs. The considerable force required to break through the internal fascia layer may propel the tip of the trocar or obturator into the adjoining organs when breakthrough of the fascia layer occurs. Even with blunt tip trochars and obturators that do not have cutting surfaces or blades, there is a risk of damage to the adjacent internal organs.
To accomplish minimally invasive bladder surgery, it is necessary to penetrate the bladder wall to gain access to the interior of the bladder. Penetrating the bladder wall with a trocar or obturator is difficult because the bladder wall is very flaccid and easily deformable and movable. The bladder wall offers very little reactive resistance to force applied during blunt force dilation, regardless of whether or not a small surgical pathway has been made initially through the bladder wall. In response to blunt dilation force, it is typical that the bladder wall depresses and moves away from the tip of the trocar or obturator and/or deflect sideways from the initial position, even when the initial small surgical pathway has been formed in the bladder wall. The lack of significant reactive resistance from the bladder wall itself makes it is very difficult to penetrate the bladder wall from the outside to the inside of the bladder, which of course is the direction of penetration for enlarging the opening to insert the cannula. Even when penetration is achieved, that penetration may occur in a location different from that desired or at a location separated from the initial small surgical incision, due to the sideways deflection of the bladder wall.
To attempt to make the bladder wall more resistant to deflection and sideways movement, the bladder may be filled with fluid to distend the bladder wall. The distension fluid creates a reactive resistance to movement of the bladder wall, and allows penetration to be more effectively accomplished at the desired location. However, making an initial small surgical pathway or incision through the bladder wall prior to expanding that small pathway causes the distention fluid to leak from the bladder, thereby losing most of the benefit derived from fluid distention.
U.S. Pat. No. 8,118,826, which is assigned to the assignee hereof, describes an advantageous procedure for making an initial small surgical pathway starting inside the bladder and progressing outward through the bladder wall and the abdominal wall to the external skin. Such an inside-out incision is relatively more controllable because the bladder wall is pushed against the more reactively resistant abdominal wall. A cutting element readily pierces through the bladder wall and the abdominal wall to create the initial small surgical pathway. However, if the initial alignment of the surgical pathway through the bladder wall and the abdominal wall is lost, as it will be if the advancement member which makes the inside-out initial small surgical pathway is withdrawn from that pathway, it is virtually impossible to regain the alignment of the small pathways through the bladder wall and the abdominal wall to facilitate enlarging the small pathway with outside-in blunt force dilation. Attempts to regain the alignment are resisted by the flaccid nature of the bladder wall which easily shifts sideways relative to the location of the small pathway in the more stable abdominal wall. Under such circumstances, when penetration of the bladder wall is finally achieved, the penetration may occur in a different position from the small surgical pathway initially made through the bladder wall.
Thus, forming the initial small surgical pathway through the bladder wall does not facilitate enlargement of that opening, but instead may result in creating an extra opening through the bladder wall. Even if the alignment of the initial surgical pathways through the bladder wall and abdominal wall is maintained, the flaccid nature of the bladder wall may cause it to deform in response to the blunt force from a trocar or obturator, thereby distorting the location of the enlarged opening in the bladder wall.